1. Field of the Invention
The present invention is related to minimally invasive devices and methods for treatment of biological tissue. More particularly, the invention relates to medical procedures mediated by diode laser induced vapor/plasma in order to achieve specific effects on tissues.
2. State of the Art Statement
Since laser technology was introduced in markets for medical procedures, numerous laser devices have been proposed for tissue removal. Laser energy can be used taking advantage of its different advantageous features. As a consequence, tissue can be vaporized, liquefied, coagulated, etc, through laser radiation by means of using different treatment parameters, such as energy, power, wavelength, etc.
Laser energy can also lead to plasma formation, by means of using appropriate radiation parameters and environment properties. Plasma formation is achieved through optical breakdown, which is a non linear effect produced when laser radiation is sufficiently condensed in time and space, leading to high density power. During optical breakdown of electromagnetic energy, an ionized state or plasma is formed. Plasma expands rapidly generating a shockwave which may be followed by cavitation or vapor bubble formation. Cavitation or vapor bubble collapse further contributes to shockwave generation. As a consequence, by focusing laser energy on a target material such as a gas, liquid or solid, the latter may be damaged by the sequence of optical breakdown, plasma formation and shockwave generation. Plasma and cavitation phenomena are both associated with strong photo and thermo-ablative effects. Inside plasma bubbles, high temperatures of over a thousand degrees arise. The presence of cavitation effects is always associated with a typical crackling noise produced by the shockwaves. One example of how this can be achieved is by providing an initial pulse as for instance in the FREDDY device (in this case generated by a flash lamp pumped frequency doubled pulsed YAG laser). The plasma produced by FREDDY laser is a sparkling plasma.
According to the afore-mentioned mechanism of action, laser energy can be applied in two different ways to achieve tissue removal (by means of plasma formation). Indirectly, by focusing it upon a target placed between laser beam and tissue, which in turn vibrates due to optical breakdown and emulsifies tissue, or directly on target tissue in order to achieve its removal.
In the first case, laser energy is transmitted through an optical fiber generating a shockwave which produces vibrational motion in the target (placed at a handpiece's tip) that is then transmitted to the tissue in order to cause emulsification.
In U.S. Pat. No. 5,224,942, Beuchat et al. disclose a method and apparatus using laser energy for destroying body tissue which includes a handpiece comprising a surgical tip assembly which is driven by means of laser to achieve optical breakdown, plasma formation and shockwave generation to emulsify or destroy body tissue. As laser is focused on a target (placed inside the handpiece) which vibrates due to plasma formation, mild energy is applied to tissue, which is only emulsified by mechanical vibration of handpiece tip. As a consequence, versatility of this system is limited as it is aimed at treating soft tissue.
U.S. Pat. No. 5,324,282 by Dodick et al., teaches a system based on similar principles. Pulsed laser energy is discharged to strike a metal target, which acts as a transducer converting the electromagnetic energy to shockwaves that are directed to tissue to be treated. The mechanical shockwaves cause the tissue to fracture.
In U.S. Patent Application No. 2004/0167504, Thyzel et al. disclose a surgical needle for fracturing tissue comprising a distal operating port which holds tissue. Pulsed laser energy is applied to a target through an optical fiber, generating shockwaves due to plasma formation from the optical breakdown of target, impinging on the tissue to be fractured. This patent is mainly focused on fracturing tissue, so here again system versatility is limited.
Afore-mentioned patents are founded on plasma formation upon a target material, which converts optical breakdown into mechanical vibrations. As a consequence, energy loss occurs in this transduction, diminishing treatment efficacy. Furthermore, mechanical vibrations are not selective with the tissue to be treated, so effects on other tissue rather than tissue to be treated may appear. In other words, not only desired tissue may be affected by vibrations.
When laser radiation is directly focused on tissue in order to achieve its removal, target for radiation is now tissue itself. Usually, tissue to be removed is surrounded by liquid and illuminated with laser radiation above a threshold intensity level, generating a shockwave. Thus, tissue is damaged by mechanical energy, rather than melting. This method is widely used in order to break calculi, stones, and calcified tissue within the body. For instance, plasma has been used in medical treatments in the form of ionized Argon gas for the ablation of mucosal layers. This way stones have been fractured by the shockwaves created due to the collapse of bubbles initiated by plasma formation at the tip of fiber optics delivering laser pulses from flash lamp pumped, frequency doubled YAG lasers (FREDDY).
In U.S. Pat. No. 5,071,422, Watson et al. disclose a method for breaking down material within the body, based on a pulsed dye laser source. Optical fiber is inserted in the area to be treated, which is surrounded with liquid and then radiated with pulsed dye laser energy in order to achieve fragmentation by means of shockwaves. This invention basically discloses calculi and stone fragmentation. But if dye laser radiation is not absorbed by stones, plasma formation will not occur and laser lithotripsy will not be effective. The plasma produced by a dye laser is sparkling plasma. Furthermore, as a pulsed dye laser source is used, frequent maintenance may be required as this source is not a solid-state laser.
U.S. Pat. No. 5,963,575 by Müller et al., discloses a Q-switched laser system for laser lithotripsy. The system incorporates longer pulse duration, increasing plasma formation and consequently shockwave production. Laser source is preferably a Nd:YAG laser, which is a ionic crystal source. As a consequence, it has low efficiency, large dimensions, and needs liquid cooling. Moreover, it requires alignment, as laser radiation is conveyed to the treatment zone by means of mirrors instead of optical fibers. Furthermore, this technology lacks precision compared to other laser technologies.
In U.S. Pat. No. 4,960,108, Reichel et al. teach a laser-induced lithotripter in which pulsed laser radiation in the vicinity of infrared region is concentrated at a concrement to be destroyed which is surrounded with an aqueous rinsing liquid. Concrement is destroyed by breakdown (plasma) of rinsing liquid, giving rise to shockwave and cavitation. Rinsing liquid includes a metal compound which lowers the energy required for said breakdown.
All previous-mentioned patents only disclose use of laser sources that may be usually voluminous, inaccurate, inefficient and/or requiring frequent maintenance.
Due to the disadvantages and lack of versatility of current plasma formation techniques, a need exists for a device that provides a fast and safe alternative to address their shortcomings.